Japanese Patent Laying-Open No. 2000-274693 (Patent Document 1) is a prior art document that discloses a cooking device having a uniform gap between a box and a door to communicatively connect the outside of a heating chamber with the inside of the heating chamber when the door for opening/closing the heating chamber is closed.
In the cooking device described in Patent Document 1, when high-frequency heating is started, an exhaust fan motor is driven to reduce the atmospheric pressure in the heating chamber, causing outside air to be sucked into the heating chamber through the gap. Due to the sucked outside air, a large amount of vapor produced by high-frequency heating from the object being cooked in the heating chamber cannot come close to the door on the front of the heating chamber. As a result, fogging of the sight glass on the door is prevented.